Street Lighting and Blue Light, Frequently Asked Questions

In the last two decades, the medical research community has learned much about light’s role in the physiology of plants and animals,8 some of which has focused on the influence of short-wavelength light. Researchers have demonstrated, for example, the ability of such light to affect circadian rhythm (the 24-hour “biological clock”). Humans and other organisms have evolved this biological response to regular periods of daylight and darkness. In the early 2000s, researchers were able to identify a class of previously unknown photoreceptors, the ipRGCs (see “What are the five types of photoreceptor in the human eye, and what is an action spectrum?”) that links directly to parts of the brain outside the visual cortex. The peak sensitivity of this type of photoreceptor in a 32-year old male is at approximately 490 nm, with the raw sensitivity of its photopigment (melanopsin) at around 480 nm.10 Both of these peaks fall at the upper end of the range commonly described as “blue.”

Simultaneously with the rise in our understanding of nonvisual photoreception, LEDs have emerged as a viable light source for general illumination. Because of the rise in use of white LEDs for outdoor lighting, and their relatively greater short-wavelength content compared to the high-pressure sodium (HPS) products they’re typically replacing, concerns have arisen that the potentially increased presence of short wavelengths in the night environment may be detrimental to health.